1. Field of the Invention
The present invention relates to a lens driving mechanism for moving a lens in its optical axis direction.
2. Related Background Art
As a conventional lens driving mechanism, a mechanism shown in, e.g., FIG. 28 is known.
The lens driving mechanism comprises a lens frame 53 for holding a lens 54, a guide shaft 52 for guiding the lens frame 53 to be movable in the optical axis direction of the lens 54, a motor 55 having a rotating output shaft, a feed screw 59 which extends in a direction parallel to an optical axis C and is formed with a male screw on its outer circumferential surface, a nut member 58 formed with a female screw which meshes with the feed screw 59, and a stationary cylinder 51 which covers these members. The nut member 58 is buried in the lens frame 53, and moves integrally with the lens 54 and the lens frame 53. When the feed screw 59 rotates upon driving the motor 55, the nut member 58 moves in the direction parallel to the optical axis C, and the lens frame 53 and the lens 54 move in the optical axis direction upon movement of the nut member 58.
However, in the prior art, the nut member 58, the feed screw 59, and the like are required for moving the lens 54 in the optical axis direction, and the number of parts increases unwontedly. Furthermore, since the lens frame 53 is securely guided by the guide shaft 52 to accurately move in the optical axis direction alone, smooth rotation of the feed screw 59 is disturbed in association with the nut member 58 unless the feed screw 59 is accurately set to be parallel to the optical axis C, resulting in a heavy load on the motor 55. That is, unless the relative positional relationship among the nut member 58, the feed screw 59, and the motor 55 is determined with very high precision, an unwanted constraint force is produced, and a heavy load acts on the motor 55. As described above, since the prior art requires a large number of parts and high assembly precision, a large number of assembly steps is required.